Correction factor signals for cathode ray tubes

Abstract

A method of convergence correction in a three beam color cathode ray tube dividing the screen into a plurality of discrete areas. Digital values for convergence factor signals are derived for a predetermined number of the discrete areas and a spreading algorithm is used to derive digital values for the remaining areas. The resulting digital values are stored in a digital store and used to provide convergence correction factor signals during operation of the tube.

Having thus described my invention, what I claim as new, and desire to secure by Letters Patent is: 
     
       1. In cathode ray tube apparatus in which the screen is notionally divided into a plurality of areas and which includes storage means arranged in operation to contain correction factor signals for each area of the screen, the method of generating correction factor signals comprising the steps of displaying test patterns at a number of points of the screen less than the number of said areas, adjusting the displayed test patterns to remove distortions thereof, deriving correction factor signals for the points at which the test patterns are displayed in accordance with the adjustments effected, and using the derived correction factor signals to determine correction factor signals for each area of the screen. 
     
     
       2. A cathode ray tube display system for performing the method of claim 1, including a keyboard, a processor, storage means and control logic means arranged to accept operator entries at said keyboard for registering said derived signal values and to generate said determined signal values according to an interpolating algorithm.   
     
     
       3. The method of claim 1, including the steps of displaying the test patterns for different points sequentially, the adjustment of a display test pattern, determining correction factor signals for at least some areas of the screen, and accumulating for every area of the screen the correction factor signals thus determined, whereby for each area of the screen final correction factor signals are obtained which are the sums of the correction factor signals determined by the adjustment of the individual test pattern. 
     
     
       4. A method as claimed in claim 3 including the steps of displaying a test pattern at the center of the screen, deriving a correction factor value for that area and adding the derived correction factor value to the correction factor values for all other areas of the screen. 
     
     
       5. A method as claimed in claim 3 including the step of storing the derived correction factor signals in a digital store. 
     
     
       6. A method as claimed in claim 5 in which said digital store stores digital correction factor values associated with each of said plurality of areas. 
     
     
       7. The method of claim 1 or 3, wherein the cathode ray tube is a multi-gun color tube, and wherein for each area of the screen a plurality of correction factor signals are determined. 
     
     
       8. A method as claimed in claim 7, wherein the step of displaying a test pattern at a selected point is a major step and includes the steps of deriving correction factor signal values for each of three color guns and a lateral correction coil.   
     
     
       9. A method as claimed in claim 8 in which the correction factor signal values derived before a major step is entered are retained in the digital store until that major step is completed. 
     
     
       10. A method as claimed in claim 9 in which an operator may determine to move either forward to a next major step or back to a previously completed major step. 
     
     
       11. A method as claimed in claim 7 in which said points comprise screen axis end points, points intermediate of said end points and the center of the screen, and screen corner points,   and the method of determining said correction factor signals for said associated areas comprises spreading the derived correction values for said points.   
     
     
       12. A method as claimed in claim 11, wherein the derived correction factor values for the axis end points are utilized to define a parabolic distribution of determined correction factor values decreasing from the respective end point toward the screen center,   the derived values for said intermediate points are utilized to define a cubic distribution of determined correction factor values decreasing from the respective intermediate point both toward the respective axis end point and said center, and   the derived values for said corner points are utilized to define determined correction factor values decreasing linearly toward the adjacent axis end points and parabolicly toward said center,   the several correction factors being combined to yield said final correction values for said associated areas of said screen.   
     
     
       13. The method of claim 7, wherein the correction factor signals define respective deflection corrections to be applied to the red, blue, green and blue lateral convergence coils. 
     
     
       14. In cathode ray tube apparatus comprising a screen which in the operation of the apparatus is notionally divided into a plurality of areas, and storage means arranged in operation to contain correction factor signals for each area of the screen, the improvement which comprises means for generating test patterns for a number of points of the screen less than the number of said areas, means for adjusting the test patterns to remove distortions thereof, means for deriving correction factor signals for said points and generating correction signals from said derived signals for all said areas, said last named means comprising means for accumulating for every area of the screen the correction factor signals thus determined, whereby for each area of the screen final correction factor signals are obtained which are the sums of the correction factor signals determined by the adjustment of the individual test pattern, and means for recording said sums in said storage means.